1. Field of the Invention
The present invention relates to optical materials transparent in the infrared (IR) region, and, more particularly, to diamond/zinc selenide (or zinc sulfide) windows.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2.Description of Related Art
Diamond has many uses. One particular use is directed to hard, optically transparent windows. In such applications, diamond is used as a coating to provide hardness to the window for protection, for ultra-high speeds or poor environmental conditions, such as rain.
Historically, diamond-like carbon (DLC) and polycrystalline diamond coatings have been deposited on IR window materials such as germanium and germanium-coated zinc selenide or zinc sulfide to improve the hardness thereof.
Processes for depositing true diamond films are rapidly improving. Diamond has several advantages over DLC films, including greater hardness and a near-absence of the stress which limits the thickness of the DLC films. However, one process limitation, which must be overcome, is that high-quality diamond requires deposition temperatures of at least 650.degree. C. It has been observed that at temperatures above 250.degree. C., sulfur/selenium is removed from the ZnS/ZnSe substrate with a resulting decrease of internal transmittance. Additionally, the thermal coefficients of expansion for zinc salts and diamond vary by an order of magnitude. Therefore, the issue of substrate temperature is central to diamond coating of zinc salt domes.
Accordingly, there is a need in the art for an improved process for providing improved IR windows having a diamond support.